1. Field of the Invention
The present invention is directed toward a method for preparing Group II metal overbased sulfurized alkylphenols. In particular, the present invention is directed toward the discovery that the use of a sulfurization catalyst during the preparation of Group II metal overbased sulfurized alkylphenols results in a product generally characterized as having lower crude sediment, a higher Total Base Number (TBN) and lower viscosity than similar products prepared without a sulfurization catalyst.
2. Prior Art
Group II metal overbased sulfurized alkylphenols are useful lubricating oil additives which impart detergency and dispersancy properties to the lubricating oil composition as well as providing for an alkalinity reserve in the oil. Alkalinity reserve is necessary in order to neutralize acids generated during engine operation. Without this alkalinity reserve, the acids so generated would result in harmful engine corrosion.
One method of preparing Group II metal overbased sulfurized alkylphenols is described in U.S. Pat. No. 3,178,368, where an alkylphenol, a sulfonate, a high molecular weight alcohol, lubricating oil and sulfur are combined and heated with agitation. Hydrated lime is then added, the system heated and ethylene glycol added. Water of reaction is removed, the mixture cooled, and carbon dioxide added. Uncombined CO.sub.2 is removed and the reaction vessel is heated to remove ethylene glycol, water and the high molecular alcohol. The product is overbased by the incorporation therein of hydrated lime and carbon dioxide.
U.S. Pat. No. 3,367,867 discloses a similar process to that of U.S. Pat. No. 3,178,368 with the exception that this reference discloses that the use of alkyl groups on the alkylphenol which are mixtures of straight- and branched-chain alkyl results in products having suitable viscosities as well as antifoaming properties.
I have now discovered a novel method for preparing Group II metal overbased sulfurized alkylphenols. In particular, in the method of the instant invention, Group II metal overbased sulfurized alkylphenols are prepared by employing a "sulfurization catalyst" in the preparation of these additives. A particularly preferred catalyst is 2-mercaptobenzothiazole (MBT) and derivatives thereof.
To my knowledge, the use of a sulfurization catalyst in the preparation of Group II metal overbased sulfurized alkylphenols is not taught in the prior art. Prior art references include U.S. Pat. No. 4,100,085 which describes the use of ammonia or ammonium hydroxide as a promoter in the synthesis of overbased sulfurized alkylphenols. Likewise, U.S. Pat. No. 4,212,752 describes the use of certain amino promoters, such as primary and secondary alkylamines, polyalkyleneamines, amino acids, etc., in the synthesis of overbased sulfurized alkylphenols.